Question

Let say we have Class A and Class B. ClassB extends Class A. (ClassB : ClassA)

Now let’s say that whenever I instantiate ClassB, I’d like to Run some Random code and only then call “base” to reach ClassA constructor.

Like:

class ClassA
{
    public ClassA()
    {
        Console.WriteLine("Initialization");
    }  
}

class ClassB : ClassA
{
    public ClassB() //: base() 
    {
        // Using :base() as commented above, I would execute ClassA ctor before                                                         //          Console.WriteLine as it is below this line... 
        Console.WriteLine("Before new");
        //base() //Calls ClassA constructor using inheritance
        //Run some more Codes here...
    }
}

In the programming language I usually work with, I can do that, by simply calling super() after Console.WriteLine(); But I cant make it in C#. Is there any other syntax or other way to do that?

Answer 1

There’s a hacky way of doing it using an instance variable initializer:

using System;

class ClassA
{
    public ClassA()
    {
        Console.WriteLine("Initialization");
    }  
}

class ClassB : ClassA
{
    private readonly int ignoreMe = BeforeBaseConstructorCall();

    public ClassB()
    {
    }

    private static int BeforeBaseConstructorCall()
    {
        Console.WriteLine("Before new");
        return 0; // We really don't care
    }
}

class Test
{
    static void Main()
    {
        new ClassB();
    }    
}

The less hacky way of doing it is to rethink how you construct a ClassB to start with. Instead of having clients call the constructor directly, provide a static method for them to call:

public static ClassB CreateInstance()
{
    Console.WriteLine("Before initialization stuff");
    return new ClassB();
}